Along with increasing diversities in lifestyles and activity patterns of people today, advertisement videos provided by mass media and the like have significant influence on such people with diversities. The increased availability of the Internet in recent years also makes people demand for new information, and advertisement pictures or videos posted or displayed in trains, for example, are expected to have high advertising effects. Particularly due to the fact that an in-train space is confined and activities of passengers are limited, advertisement videos are considered to be highly effective as means for advertisement. Accordingly, the demand for such advertisement is rapidly growing.
Further, with the emergence of high definition videos and display devices with larger-sized screens, video data for some advertisements is now as large as 50 megabytes. Accordingly, it is desired that a storage medium for use in a train is capable of storing a large amount of video data for a long period of time. However, conditions specific to trains require a storage medium that is very expensive per unit capacity, for example, a semiconductor disk that is resistant to heat and vibration. Thus, it poses large limitations on recording of video data. Therefore, there have been taken some measures such as deleting unnecessary video data to efficiently use the storage capacity of a storage medium.
Conventionally, information providing devices disclosed in, for example, Patent Documents 1 and 2, secure a free space in a storage medium by deleting video data in chronological order, i.e., from one recorded on the storage medium at an earlier time and whose validity period has expired.    Patent Document 1: Japanese Patent Application Laid-open No. 2002-314910    Patent Document 2: Japanese Patent Application Laid-open No. 2003-110982